cmake: add CURL_DROP_UNUSED option to reduce binary sizes

To enable known linker options dropping unused, dead, code and data from the executables built. Useful to reduce binary sizes for curl, libcurl shared lib and apps linking static libcurl. It's effective on both "unity" and non-unity builds. Aligning "unity" build sizes with default, non-unity ones. Supported platforms: Apple, MSVC, llvm/clang and GCC on all tested platforms: Linux, BSDs, Windows, MSYS2/Cygwin, Android, MS-DOS. Notes: - Static libraries grow 20-30% with non-Apple toolchains. This effect is controlled by separate, optional compiler flags on non-Apple. This patch enables them automatically for public binaries (libcurl and curl tool), and leaves them off for internal/test ones. - MSVC enables this option by default for 'Release' configurations. The curl build option has no effect on it. - Observed effect on VS2010 is negligible. VS2012+ is recommended. - Works with LTO, Fil-C. - No observed/conclusive effect on build speed. - On Windows with clang/gcc (mingw-w64/MSYS2/Cygwin) it also enables `-fno-asynchronous-unwind-tables` as a workaround to make the toolchain options actually work. Ref: https://sourceware.org/bugzilla/show_bug.cgi?id=11539 Thanks-to: Andarwinux Also: - GHA: enable in Linux and MinGW jobs to test it. Size changes: - linux aws-lc H3: curl: 2000000 -> 1937152, libcurl.a: 2065724 -> 2716532 bytes - macos clang HTTP-only: curl: 1364376 -> 128799 bytes, libcurl.a: unchanged - macos llvm MultiSSL: curl: 410056 -> 405720, libcurl.dylib: 1350336 -> 1348480 bytes - mingw schannel c-ares U: curl: 1588736 -> 1507328, libcurl-d.a: 3322040 -> 3884746 bytes bld: 34 -> 35MB - GHA: enable in MSVC and Apple jobs to reduce disk footprint, with no obvious downside. Size changes: - AppVeyor CI VS2019: curl: 2339840 -> 1295872, libcurl-d.dll: 3155968 -> 1900544 bytes bld: 161 -> 97MB - AppVeyor CI VS2022 clang-cl: curl: 2933248 -> 2332160, libcurl-d.lib: 4762688 -> 5511330 bytes bld: 133 -> 121MB - AppVeyor CI VS2022 HTTP-only: curl: 3514368 -> 2177024, libcurl-d.lib: 2538420 -> 3151740 bytes bld: 137 -> 83MB - GHA intel: curl: 2629120 -> 2023424, libcurl-d.lib: 4366652 -> 5350670 bytes bld: 86 -> 69MB - GHA arm64: curl: 2832896 -> 2063872, libcurl-d.lib: 4690616 -> 5597250 bytes bld: 82 -> 66MB Refs: https://maskray.me/blog/2021-02-28-linker-garbage-collection https://web.archive.org/web/20110811230637/msdn.microsoft.com/en-us/library/bxwfs976.aspx (VS2010) https://learn.microsoft.com/cpp/build/reference/opt-optimizations https://learn.microsoft.com/cpp/build/reference/gy-enable-function-level-linking Closes #20357
2026-04-14 18:11:40 +03:00 · 2026-01-19 12:34:59 +01:00 · 2026-01-19 12:34:59 +01:00 · 66ad54e46b
commit 66ad54e46b
parent aacbe4d9bf
9 changed files with 50 additions and 8 deletions
--- a/.github/workflows/http3-linux.yml
+++ b/.github/workflows/http3-linux.yml
@ -389,7 +389,7 @@ jobs:
            tflags: '--min=1790'
            generate: >-
              -DOPENSSL_ROOT_DIR=/home/runner/awslc/build -DUSE_NGTCP2=ON -DBUILD_SHARED_LIBS=OFF
-              -DCMAKE_UNITY_BUILD=ON
+              -DCMAKE_UNITY_BUILD=ON -DCURL_DROP_UNUSED=ON

          - name: 'boringssl'
            install_steps: skipall
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@ -121,7 +121,7 @@ jobs:
            tflags: '--min=830 1 to 950'
            LDFLAGS: -Wl,-rpath,/home/runner/mbedtls/lib
            PKG_CONFIG_PATH: /home/runner/mbedtls/lib/pkgconfig
-            generate: -DCURL_USE_MBEDTLS=ON -DENABLE_DEBUG=ON -DCURL_USE_GSSAPI=ON
+            generate: -DCURL_USE_MBEDTLS=ON -DENABLE_DEBUG=ON -DCURL_USE_GSSAPI=ON -DCURL_DROP_UNUSED=ON

          - name: 'mbedtls gss valgrind 2'
            install_packages: libnghttp2-dev libidn2-dev libldap-dev libgss-dev valgrind
@ -163,7 +163,7 @@ jobs:
          - name: 'awslc'
            install_packages: libidn2-dev
            install_steps: awslc
-            generate: -DOPENSSL_ROOT_DIR=/home/runner/awslc -DUSE_ECH=ON -DCMAKE_UNITY_BUILD=OFF
+            generate: -DOPENSSL_ROOT_DIR=/home/runner/awslc -DUSE_ECH=ON -DCMAKE_UNITY_BUILD=OFF -DCURL_DROP_UNUSED=ON

          - name: 'boringssl'
            install_steps: boringssl pytest
--- a/.github/workflows/macos.yml
+++ b/.github/workflows/macos.yml
@ -151,7 +151,7 @@ jobs:
            # https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#cross-compiling-for-ios-tvos-visionos-or-watchos
            [ -n "${MATRIX_GENERATOR}" ] && options="-G ${MATRIX_GENERATOR}"
            cmake -B bld -G Ninja -D_CURL_PREFILL=ON \
-              -DCMAKE_UNITY_BUILD=ON -DCURL_WERROR=ON \
+              -DCMAKE_UNITY_BUILD=ON -DCURL_DROP_UNUSED=ON -DCURL_WERROR=ON \
              -DCMAKE_SYSTEM_NAME=iOS \
              -DUSE_APPLE_IDN=ON \
              ${MATRIX_GENERATE} ${options}
@ -417,7 +417,7 @@ jobs:
              [ "${_chkprefill}" = '_chkprefill' ] && options+=' -D_CURL_PREFILL=OFF'
              cmake -B "bld${_chkprefill}" -G Ninja -D_CURL_PREFILL=ON \
                -DCMAKE_INSTALL_PREFIX="$HOME"/curl-install \
-                -DCMAKE_UNITY_BUILD=ON -DCURL_WERROR=ON \
+                -DCMAKE_UNITY_BUILD=ON -DCURL_DROP_UNUSED=ON -DCURL_WERROR=ON \
                -DCMAKE_OSX_SYSROOT="${sysroot}" \
                -DCMAKE_C_COMPILER_TARGET="$(uname -m | sed 's/arm64/aarch64e/')-apple-darwin$(uname -r)" \
                ${MATRIX_GENERATE} ${options}
@ -652,7 +652,7 @@ jobs:
            [ -n "${MATRIX_MACOS_VERSION_MIN}" ] && options+=" -DCMAKE_OSX_DEPLOYMENT_TARGET=${MATRIX_MACOS_VERSION_MIN}"
            # would pick up nghttp2, libidn2, and libssh2
            cmake -B bld -G Ninja -D_CURL_PREFILL=ON \
-              -DCMAKE_UNITY_BUILD=ON -DCURL_WERROR=ON \
+              -DCMAKE_UNITY_BUILD=ON -DCURL_DROP_UNUSED=ON -DCURL_WERROR=ON \
              -DCMAKE_OSX_SYSROOT="${sysroot}" \
              -DCMAKE_C_COMPILER_TARGET="$(uname -m | sed 's/arm64/aarch64e/')-apple-darwin$(uname -r)" \
              -DCMAKE_IGNORE_PREFIX_PATH=/opt/homebrew \
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@ -204,7 +204,7 @@ jobs:
          # MinGW
          - { build: 'autotools', sys: 'mingw64'   , env: 'x86_64'       , tflags: 'skiprun'   , config: '--enable-debug --with-openssl --disable-threaded-resolver --enable-static --without-zlib', install: 'mingw-w64-x86_64-openssl mingw-w64-x86_64-libssh2', name: 'default' }
          - { build: 'autotools', sys: 'mingw64'   , env: 'x86_64'       , tflags: ''          , config: '--enable-debug --with-openssl --enable-windows-unicode --enable-ares --enable-static --disable-shared --enable-ca-native', install: 'mingw-w64-x86_64-c-ares mingw-w64-x86_64-openssl mingw-w64-x86_64-nghttp3 mingw-w64-x86_64-libssh2', name: 'c-ares U' }
-          - { build: 'cmake'    , sys: 'mingw64'   , env: 'x86_64'       , tflags: '--min=1650', config: '-DENABLE_DEBUG=ON  -DBUILD_SHARED_LIBS=OFF -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON -DENABLE_ARES=ON', install: 'mingw-w64-x86_64-c-ares mingw-w64-x86_64-libssh2', type: 'Debug', name: 'schannel c-ares U' }
+          - { build: 'cmake'    , sys: 'mingw64'   , env: 'x86_64'       , tflags: '--min=1650', config: '-DENABLE_DEBUG=ON  -DBUILD_SHARED_LIBS=OFF -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON -DENABLE_ARES=ON -DCURL_DROP_UNUSED=ON', install: 'mingw-w64-x86_64-c-ares mingw-w64-x86_64-libssh2', type: 'Debug', name: 'schannel c-ares U' }
          # MinGW torture
          - { build: 'cmake'    , sys: 'mingw64'   , env: 'x86_64'       , tflags: '-t --shallow=13 --min=700 1 to 950'   , config: '-DENABLE_DEBUG=ON  -DBUILD_SHARED_LIBS=OFF -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON -DENABLE_ARES=ON', install: 'mingw-w64-x86_64-c-ares mingw-w64-x86_64-libssh2', type: 'Debug', name: 'schannel U torture 1' }
          - { build: 'cmake'    , sys: 'mingw64'   , env: 'x86_64'       , tflags: '-t --shallow=13 --min=700 951 to 9999', config: '-DENABLE_DEBUG=ON  -DBUILD_SHARED_LIBS=OFF -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON -DENABLE_ARES=ON', install: 'mingw-w64-x86_64-c-ares mingw-w64-x86_64-libssh2', type: 'Debug', name: 'schannel U torture 2' }
@ -213,7 +213,7 @@ jobs:
          #          Windows. Do not use this component till there is a fix for these.
          # https://github.com/curl/curl-for-win/blob/3951808deb04df9489ee17430f236ed54436f81a/libssh.sh#L6-L8
          - { build: 'cmake'    , sys: 'clang64'   , env: 'clang-x86_64' , tflags: ''          , config: '-DENABLE_DEBUG=ON  -DBUILD_SHARED_LIBS=OFF -DCURL_USE_GNUTLS=ON   -DENABLE_UNICODE=OFF -DUSE_NGTCP2=ON -DCURL_USE_LIBSSH2=OFF -DCURL_USE_LIBSSH=ON', install: 'mingw-w64-clang-x86_64-gnutls mingw-w64-clang-x86_64-nghttp3 mingw-w64-clang-x86_64-ngtcp2 mingw-w64-clang-x86_64-libssh', type: 'Debug', name: 'gnutls libssh' }
-          - { build: 'cmake'    , sys: 'clangarm64', env: 'clang-aarch64', tflags: 'skiprun'   , config: '-DENABLE_DEBUG=OFF -DBUILD_SHARED_LIBS=ON  -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON', install: 'mingw-w64-clang-aarch64-libssh2', type: 'Release', name: 'schannel R', image: 'windows-11-arm' }
+          - { build: 'cmake'    , sys: 'clangarm64', env: 'clang-aarch64', tflags: 'skiprun'   , config: '-DENABLE_DEBUG=OFF -DBUILD_SHARED_LIBS=ON  -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON -DCURL_DROP_UNUSED=ON', install: 'mingw-w64-clang-aarch64-libssh2', type: 'Release', name: 'schannel R', image: 'windows-11-arm' }
          - { build: 'cmake'    , sys: 'clang64'   , env: 'clang-x86_64' , tflags: 'skiprun'   , config: '-DENABLE_DEBUG=ON  -DBUILD_SHARED_LIBS=OFF -DCURL_USE_OPENSSL=ON  -DENABLE_UNICODE=OFF -DUSE_NGTCP2=ON', install: 'mingw-w64-clang-x86_64-openssl mingw-w64-clang-x86_64-nghttp3 mingw-w64-clang-x86_64-ngtcp2 mingw-w64-clang-x86_64-libssh2', type: 'Release', name: 'openssl', chkprefill: '_chkprefill' }
          - { build: 'cmake'    , sys: 'ucrt64'    , env: 'ucrt-x86_64'  , tflags: 'skiprun'   , config: '-DENABLE_DEBUG=OFF -DBUILD_SHARED_LIBS=ON  -DCURL_USE_OPENSSL=ON', install: 'mingw-w64-ucrt-x86_64-openssl mingw-w64-ucrt-x86_64-libssh2', type: 'Release', test: 'uwp', name: 'schannel' }
          # { build: 'autotools', sys: 'ucrt64'    , env: 'ucrt-x86_64'  , tflags: 'skiprun'   , config: '--without-debug --with-schannel --disable-static', install: 'mingw-w64-ucrt-x86_64-libssh2', type: 'Release', test: 'uwp', name: 'schannel' }
@ -528,6 +528,7 @@ jobs:
              -DCMAKE_C_COMPILER=gcc \
              -DCMAKE_BUILD_TYPE="${MATRIX_TYPE}" \
              -DCMAKE_UNITY_BUILD=ON -DCMAKE_UNITY_BUILD_BATCH_SIZE=30 \
+              -DCURL_DROP_UNUSED=ON \
              -DCURL_WERROR=ON \
              -DUSE_LIBIDN2=OFF \
              ${MATRIX_CONFIG}
@ -891,6 +892,7 @@ jobs:
              -DCMAKE_EXE_LINKER_FLAGS="-INCREMENTAL:NO ${ldflags}" \
              -DCMAKE_SHARED_LINKER_FLAGS="-INCREMENTAL:NO ${ldflags}" \
              -DCMAKE_UNITY_BUILD=ON \
+              -DCURL_DROP_UNUSED=ON \
              -DCURL_WERROR=ON \
              -DLIBPSL_INCLUDE_DIR="${MINGW_PREFIX}/include" \
              -DLIBPSL_LIBRARY="${MINGW_PREFIX}/lib/libpsl.dll.a" \
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@ -300,6 +300,40 @@ if(CURL_CODE_COVERAGE)
  endif()
 endif()

+set(CURL_CFLAGS "")  # C flags set for libcurl and curl tool (aka public binaries) only
+
+option(CURL_DROP_UNUSED "Drop unused code and data from built binaries" OFF)
+if(CURL_DROP_UNUSED OR TRUE)
+  if(APPLE)
+    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)
+      set_property(DIRECTORY APPEND PROPERTY LINK_OPTIONS "-Wl,-dead_strip")
+    else()
+      set_property(DIRECTORY APPEND PROPERTY LINK_FLAGS "-Wl,-dead_strip")
+    endif()
+  elseif(MSVC)  # Options below are toolchain defaults in Release configurations.
+    # This option does not seem to have an effect with VS2010:
+    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)
+      set_property(DIRECTORY APPEND PROPERTY LINK_OPTIONS "-OPT:REF")
+    else()
+      set_property(DIRECTORY APPEND PROPERTY LINK_FLAGS "-OPT:REF")
+    endif()
+    # Optional, but reduces binary size further, with the cost of larger objects/static libraries:
+    list(APPEND CURL_CFLAGS "-Gy")
+  elseif(CMAKE_C_COMPILER_ID STREQUAL "GNU" OR CMAKE_C_COMPILER_ID MATCHES "Clang")
+    if(WIN32)
+      # To make -Wl,--gc-sections work on Windows: https://sourceware.org/bugzilla/show_bug.cgi?id=11539
+      set_property(DIRECTORY APPEND PROPERTY COMPILE_OPTIONS "-fno-asynchronous-unwind-tables")
+    endif()
+    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)
+      set_property(DIRECTORY APPEND PROPERTY LINK_OPTIONS "-Wl,--gc-sections")
+    else()
+      set_property(DIRECTORY APPEND PROPERTY LINK_FLAGS "-Wl,--gc-sections")
+    endif()
+    # Optional, but reduces binary size further, with the cost of larger objects/static libraries:
+    list(APPEND CURL_CFLAGS "-ffunction-sections" "-fdata-sections")
+  endif()
+endif()
+
 # For debug libs and exes, add "-d" postfix
 if(NOT DEFINED CMAKE_DEBUG_POSTFIX)
  set(CMAKE_DEBUG_POSTFIX "-d")
--- a/appveyor.sh
+++ b/appveyor.sh
@ -87,6 +87,7 @@ if [ -n "${CMAKE_GENERATOR:-}" ]; then
    time cmake -G "${CMAKE_GENERATOR}" \
      -DENABLE_DEBUG=ON -DCURL_WERROR=ON \
      -DCURL_STATIC_CRT=ON \
+      -DCURL_DROP_UNUSED=ON \
      -DCURL_USE_SCHANNEL=ON -DCURL_USE_LIBPSL=OFF \
      ${CMAKE_GENERATE:-} \
      ${options} \
--- a/docs/INSTALL-CMAKE.md
+++ b/docs/INSTALL-CMAKE.md
@ -243,6 +243,7 @@ target_link_libraries(my_target PRIVATE CURL::libcurl)
 - `CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX`:  Override default versioned symbol prefix. Default: `<TLS-BACKEND>_` or `MULTISSL_`
 - `CURL_LINT`:                              Run lint checks while building. Default: `OFF`
 - `CURL_LTO`:                               Enable compiler Link Time Optimizations. Default: `OFF`
+- `CURL_DROP_UNUSED`:                       Drop unused code and data from built binaries. Default: `OFF`
 - `CURL_STATIC_CRT`:                        Build libcurl with static CRT with MSVC (`/MT`) (requires UCRT, static libcurl or no curl executable). Default: `OFF`
 - `CURL_TARGET_WINDOWS_VERSION`:            Minimum target Windows version as hex string.
 - `CURL_WERROR`:                            Turn compiler warnings into errors. Default: `OFF`
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@ -111,6 +111,7 @@ if(SHARE_LIB_OBJECT AND CMAKE_VERSION VERSION_GREATER_EQUAL 3.12)
  target_link_libraries(${LIB_OBJECT} PRIVATE ${CURL_LIBS})
  set_target_properties(${LIB_OBJECT} PROPERTIES
    POSITION_INDEPENDENT_CODE ON)
+  set_property(TARGET ${LIB_OBJECT} APPEND PROPERTY COMPILE_OPTIONS "${CURL_CFLAGS}")
  if(CURL_HIDES_PRIVATE_SYMBOLS)
    set_property(TARGET ${LIB_OBJECT} APPEND PROPERTY COMPILE_OPTIONS "${CURL_CFLAG_SYMBOLS_HIDE}")
    set_property(TARGET ${LIB_OBJECT} APPEND PROPERTY COMPILE_DEFINITIONS "CURL_HIDDEN_SYMBOLS")
@ -152,6 +153,7 @@ if(BUILD_STATIC_LIBS)
    PREFIX "" OUTPUT_NAME "${LIBCURL_OUTPUT_NAME}"
    SUFFIX "${STATIC_LIB_SUFFIX}${CMAKE_STATIC_LIBRARY_SUFFIX}"
    INTERFACE_COMPILE_DEFINITIONS "CURL_STATICLIB")
+  set_property(TARGET ${LIB_STATIC} APPEND PROPERTY COMPILE_OPTIONS "${CURL_CFLAGS}")
  if(CURL_HIDES_PRIVATE_SYMBOLS)
    set_property(TARGET ${LIB_STATIC} APPEND PROPERTY COMPILE_OPTIONS "${CURL_CFLAG_SYMBOLS_HIDE}")
    set_property(TARGET ${LIB_STATIC} APPEND PROPERTY COMPILE_DEFINITIONS "CURL_HIDDEN_SYMBOLS")
@ -213,6 +215,7 @@ if(BUILD_SHARED_LIBS)
    PREFIX "" OUTPUT_NAME "${LIBCURL_OUTPUT_NAME}"
    IMPORT_PREFIX "" IMPORT_SUFFIX "${IMPORT_LIB_SUFFIX}${CMAKE_IMPORT_LIBRARY_SUFFIX}"
    POSITION_INDEPENDENT_CODE ON)
+  set_property(TARGET ${LIB_SHARED} APPEND PROPERTY COMPILE_OPTIONS "${CURL_CFLAGS}")
  if(CURL_HIDES_PRIVATE_SYMBOLS)
    set_property(TARGET ${LIB_SHARED} APPEND PROPERTY COMPILE_OPTIONS "${CURL_CFLAG_SYMBOLS_HIDE}")
    set_property(TARGET ${LIB_SHARED} APPEND PROPERTY COMPILE_DEFINITIONS "CURL_HIDDEN_SYMBOLS")
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@ -105,6 +105,7 @@ set_property(DIRECTORY APPEND PROPERTY INCLUDE_DIRECTORIES
 add_executable(${EXE_NAME} ${CURL_CFILES} ${CURL_HFILES} ${_curl_cfiles_gen} ${_curl_hfiles_gen} ${CURLX_CFILES} ${CURLX_HFILES})
 target_compile_definitions(${EXE_NAME} PRIVATE ${_curl_definitions})
 target_link_libraries(${EXE_NAME} ${LIB_SELECTED_FOR_EXE} ${CURL_LIBS})
+set_property(TARGET ${EXE_NAME} APPEND PROPERTY COMPILE_OPTIONS "${CURL_CFLAGS}")

 add_executable(${PROJECT_NAME}::${EXE_NAME} ALIAS ${EXE_NAME})